Identification of a new pseudo-binary hydroxide during calendar corrosion of (La, Mg)2Ni7-type hydrogen storage alloys for Nickel–Metal Hydride batteries

Abstract

To improve the performances of Nickel-Metal Hydride batteries, an important step is the understanding of the corrosion processes that take place in the electrode material. In particular, the present study focuses for the first time on the model (La,Mg) 2 Ni 7 system. The calendar corrosion in 8.7M KOH medium was investigated from 6 hours to 16 weeks immersion. By a unique combination of structural and elemental characterisations, the corrosion products are evidenced in those systems. In particular, we demonstrate that Ni and Mg combine in a pseudo-binary hydroxide Mg 1-x Ni x (OH) 2 whereas La corrodes into nanoporous La(OH) 3 needles with inner hollow nanochannels.

Influence of Zr Addition on Structure and Performance of Rare Earth Mg-Based Alloys as Anodes in Ni/MH Battery

“…As we all know, the capacity fading is mainly resulting from the particle pulverization upon cycling and the surface oxidation and/or corrosion of Mg, Ni and La elements [29]. In the La-Mg-Ni system, Mg and Ni were involved in a mixed hydroxide of (Mg, Ni)(OH) 2 and La transformed into nanoporous La(OH) 3 needles [30]. The cycling improvement in this study could be related to the fact that the extent of oxidation/corrosion of Mg and La is reduced because ZrO 2 was formed as a passive film on anode surface.…”

Electrochemical hydrogenation properties of LaNi4.6Zn0.4−Sn alloys

“…More details relating electrochemical measurement procedure can be found in our previously published papers [6,7,[12][13][14][15][16][17][18][19]]. …”

“…Due to storage material activation in some first cycles, the capacity fade usually appears after 10 -15 charge/discharge cycles [16,17]. We believe that amphoteric elements increase porosity of passive layers formed on hydride material particles due to partial dissolution of their oxides in alkaline solutions and, as a consequence, improve transport-and catalytic properties of active material surface with respect to hydrogen charge/discharge process [12][13][14][15][16][17][18][19].…”

“…create nanoporous needles of La(OH) 3 with inner hollow nanochannels [14]. Alhough Ni(II) oxide or hydroxide undergo reduction in the charge cycle (reversible corrosion of nickel [6,10]), the La and Mg oxidation products cumulate in the electrode interior.…”

Phase Structure and Electrochemical Characteristics of Rhombohedral Super-Stacking La0.77Mg0.23Ni3.72Hydrogen Storage Alloy

“…2 In recent years, ternary rare earth (RE)-Mg-Ni-based hydrogen storage alloys have attracted much attention as promising candidates to replace AB 5 -type alloys owing to their remarkable discharge capacity and high-rate dischargeability. [3][4][5] The ternary RE-Mg-Ni x (2 < x < 4) alloys have layered AB 3.0 , AB 3.5 , and AB 3.8 structures, where [AB 5 ] and [A 2 B 4 ] units are alternatively stacked along the c axis with different proportions. 6,7 Each structure has an allotrope with either a hexagonal (2H) structure with MgZn 2 -type Laves subunits or a rhombohedral (3R) structure with MgCu 2 -type Laves subunits, e.g., CeNi 3 -type (2H) and PuNi 3 -type (3R), Ce 2 Ni 7 -type (2H) and Gd 2 Co 7 -type (3R), and Pr 5 Co 19 -type (2H) and Ce 5 Co 19 -type (3R) structures.…”